The invention relates to fluorochemical surfactants including those derived from nonafluorobutanesulfonyl fluoride (PBSF) that have been found to be as effective as the known premier surfactants derived from perfluorooctanesulfonyl fluoride (POSF) and can be produced at lower costs.
The art of surfactants, particularly surfactants with fluorochemical chains, shows a preference for such surfactants with longer fluorochemical chains, e.g., C6-C10 in U.S. Pat. No.2,803,615 and C6-C12 in U.S. Pat. No.3,787,351. Even in hydrocarbon surfactants, increasing the chain length of the hydrocarbon chain decreases the CMC (critical micelle concentration); the decrease in CMC is roughly one order of magnitude for each xe2x80x94CH2CH2xe2x80x94 added to the chain (Amphoteric Surfactants, edited by Eric G. Lomax, Marcel Dekker Inc. (1996), p. 13). The same trend has been noted in surfactants derived from the perfluorocarboxylic acids and sulfonic acids (Organofluorine Chemicals and their Industrial Applications, edited by R. E. Banks, Ellis Horwood Ltd. (1979), p. 56; J. O. Hendrichs, Ind. Eng Chem, 45, 1953, p. 103; M. K. Bernett and W. A. Zisman, J. Phys. Chem., 63, 1959, p. 1912). Data exist that suggest that only after the seven outermost carbon atoms are fully fluorinated do the contact angles of various liquids on the surface approach those of a perfluoro fatty acid monolayer (N. O. Brace, J. Org. Chem., 27, 1962, p. 4491; W. A. Zisman, Advan. Chem. 1964, p. 22). Since models to explain the actions of surfactants often invoke the monolayer of the surfactant on the air/liquid interface, one would expect the same to be true of fluorinated surfactants, and that activity of the surfactant is closely tied to its chain length.
We have found the same trend when the surface tensions of C4F9SO3K and C8F17SO3K were measured in water. The results are shown in FIG. 1. We have also found that the same trend can be observed in a series of homologous fluorinated glycamide salts shown in FIG. 2. In each case the surface tension of the resulting solution of the C4F9SO2Nxe2x80x94 containing surfactant was significantly higher at the same concentration than the C8F17SO2Nxe2x80x94 containing surfactant. Based on the above, use of a C4F9SO2Nxe2x80x94 containing surfactant in an application would be disadvantageous over a C8F17SO2Nxe2x80x94 containing surfactant because higher levels would be required and the end result would potentially be higher expense and adverse effects on the properties of the composition used in the application.
We have found that polymeric fluorochemical surfactants with shorter perfluoroalkyl segments, preferably those derived from perfluorobutanesulfonyl fluoride (PBSF), have surface activities that surprisingly rival that of the homologs made from perfluorooctane segments such as perfluorooctanesulfonyl fluoride (POSF). It is particularly advantageous to use PBSF in a surfactant over POSF because of the higher yield of perfluorobutanesulfonyl fluoride (58%) in electrochemical fluorination over perfluorooctanesulfonyl fluoride (31%) (Preparation, Properties, and Industrial Applications of Organofluorine Compounds, edited by R. E. Banks, Ellis Horwood Ltd (1982), p. 37). A significant advantage of PBSF derived surfactants over the more commonly used POSF derived surfactants is that they can be produced at a lower cost per weight because of their higher yields and still maintain their potency as surfactants at the same weight percent. Furthermore, even with less fluorine content, potent surfactant properties are surprisingly achieved.
Many previously known polymeric, fluorochemical surfactants contain perfluorooctyl moieties. These surfactants ultimately degrade to perfluorooctyl-containing compounds. It has been reported that certain perfluorooctyl-containing compounds may tend to bio-accumulate in living organisms; this tendency has been cited as a potential concern regarding some fluorochemical compounds. For example, see U.S. Pat. No. 5,688,884 (Baker et al.). As a result, there is a desire for fluorine-containing compositions which are effective in providing desired surfactant properties, and which eliminate more effectively from the body (including the tendency of the composition and its degradation products).
It is expected that the polymeric, fluorochemical surfactants of the present invention, which contain perfluorobutyl moieties, when exposed to biologic, thermal, oxidative, hydrolytic, and photolytic conditions found in the environment, will break down to various degradation products. For example, compositions comprising perfluorobutylsulfonamido moieties are expected to degrade, at least to some extent, ultimately to perfluorobutylsulfonate salts. It has been surprisingly found that perfluorobutylsulfonate, tested in the form of its potassium salt, eliminates from the body much more effectively than perfluorohexylsulfonate and even more effectively than perfluorooctylsulfonate.
Accordingly, one aspect of the present invention provides a polymeric surfactant comprising at least one unit of Formula I 
where Rf is xe2x80x94C4F9 or xe2x80x94C3F7; R and R2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; and x is an integer of at least 1. In one preferred embodiment, Rf is xe2x80x94C4F9.
Another aspect of the invention provides a polymeric surfactant prepared from the reaction products of the following monomers or oligomers:
(a) a compound of the formula 
(b) a compound selected from the group consisting of 
and optionally
(c) a compound of the formula 
where R, R1, Rxe2x80x2 and R2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; n is an integer from 2 to 10; nxe2x80x2 is an integer of 1 to 10; p is an integer of 1 to about 128 and q is an integer of 0 to about 55. M is hydrogen, a metal cation, or a protonated tertiary amine.
Another aspect of the invention provides a polymeric surfactant comprising at least one unit of Formula II: 
where the nonafluorobutanesulfonyl amido segment is part of a polymeric chain containing a polyalkyleneoxy segment. R, R1 and R2 are each independently hydrogen or alkyl of 1 to 4 carbon atoms; R3 is at least one or more straight or branched alkylene-oxy groups, linked together when more than one, having 2 to 6 carbon atoms; n is an integer from 2 to 10; and x, y and z are integers of at least 1.
The present invention also includes mixtures thereof in forms of surfactant compositions as well as methods of using the surfactants.
One embodiment of the present invention provides a method of reducing the surface tension of a liquid comprising adding to said liquid a surfactant composition of this invention. Another embodiment of the invention provides a method of increasing the wetting of a coating mixture on a substrate by adding to the coating mixture of surfactant composition of this invention. In one embodiment of the invention, the surface tension of a liquid can be reduced by adding to said liquid a surfactant mixture comprising a compound of Formula I or Formula II and a compound of Formula III 
in which R is hydrogen or alkyl of 1-4 carbon atoms; Ra is a hydrogen or an alkyl of 1 to 4 carbon atoms; and r is an integer of 2 to 20. Preferably, R and Ra are methyl and r is an integer from 4 to 10.
A more detailed description of the present invention including particular embodiments is described hereinafter.